Phytoavailablility and fractionation of cadmium and lead in vegetable farm soils in Ilorin, north-central, Nigeria

Abstract

Heavy metal dynamics, bioavailability and fractionation are of great importance to measure soil toxicity, in soil. However, reports showed that not much has been done to evaluate these parameters in vegetable farm soils in Ilorin metropolis. These parameters aid in assessing and extent of heavy metal viability in soil. Therefore, soils were collected from major vegetable farms in Ilorin metropolis, sorted, Thus, this study investigated the bioavailable Cd and Pb and their fractionation in vegetable farm soils in Ilorin metropolis. These experiments were conducted by , sequential extraction and Atomic Absorption Spectrophotometry, alongside analysis of some key soil properties. The results showed that the soil pH ranged from 6.62±0.04 to 7.18±0.03, organic matter 2.05 target heavy metals in the sampling areas were potentially bioavailable with phytoavailable concentration ranges of . The target heavy metals showed a high viability of the soluble and exchangeable form in most soils and in both seasons which would greatly contribute to their availability to plant uptake and soil toxicity. There is also a threat of oxidization of the potentially available Cd and Pb in other forms due to pH ranges of most of the studied soils. Therefore, vegetable farm soils in Ilorin metropolis are polluted with Cd and Pb and may have high risk of causing human health problems when vegetables grown on the soils are consumed; which calls for remediation of most of the soils. , 031 Ife Journal of Science vol. 23, no. 1 (2021) INTRODUCTION Heavy metals abound naturally in soil environment, as a result of processes of weathering of parent materials at levels that are regarded as trace and rarely toxic substance, and also from human anthropogenic activities (Herawati et al, 2010). Of the heavy metals that abound, cadmium (Cd) and lead (Pb) are common and widely studied contaminants because of their spectrum of use in production of lead-acid batteries, lead-based paints, automobiles, oil refineries, and antiknock in petrol (Ying et al., 2013). In terms of environmental concentration, Pb is the heavy metal closest to the level in which toxic signs manifest than any other substance (Iwegbue et al., 2013). Heavy metal distribution, dynamics and transport in soil depend significantly on their chemical forms (Debnárová and Doleţa, 2010). Once in the soil, heavy metals are adsorbed by initial fast reactions (minutes, hours), followed by slow adsorption reactions (days, years) and are, therefore, redistributed into different chemical forms with varying bioavailability, mobility and toxicity (Deng et al., 2012). Reports had shown that not all the heavy metals in the soil are readily available to plant but may become available under some environmental influences or changes such as pH, redox potential, cation exchange capacity, organic matter content and moisture content of the soil (Yadawe, 2011). The fraction of a total heavy metal content that is available for plant uptake in the soil depends strongly on the chemical form in which the metals are present (Lokeshwari and Chandrappa, 2012). Therefore, it is important to know the different forms of heavy metals in soil which will help in assessing the extent of toxicity or level of contaminations and remediation strategy of the heavy metal (Kabata-Pendias, 2004). The largest https://dx.doi.org/10.4314/ijs.v23i1.4